Titanium base alloys



United States Patent 3,052,538 TITANIUM BASE ALLOYS Robert W. J ech, Cleveland, and Edward P. Weber, Parma,

Ohio, assignors, by mesne assignments, to the United States of America as represented by the Secretary of the Navy No Drawing. Filed Apr. 21, 1960, Ser. No. 23,862

Claims. (Cl. '75-175.5)

The present invention relates to titanium alloys and a method of making same. It more particularly relates to an improved method of making alloys in which titanium is alloyed with intermetallic compounds of titanium.

Titanium alloys are unexcelled in strength to weight ratio up to approximately 800 degrees F. Above this temperature, the strength properties of titanium alloys decrease rapidly thus limiting their usefulness.

In the method of the present invention, intermetallic compounds, such as 'I'i Si TiB TiC, and TiAl, are dispersed in titanium to provide an alloy that has improved strength properties at high temperature. Intermetallic compounds are ground to a fine powder and then blended with titanium hydride in a ball milling operation. Consolidation is then accomplished by vacuum hot pressing, by cold compaction and extrusion, or by cold compaction, sintering and extrusion.

It is, therefore, a general object of the present invention to provide titanium alloys having suitable mechanical properties for application at temperatures between 800 and 1200 degrees F.

Another object of the present invention is to provide sintered titanium alloys that have good properties of strength and hardness.

Still another object of the present invention is to provide an improved method of making titanium alloys by combining finely divided intermetallic compounds with titanium hydride.

Other objects and advantages of the present invention will be apparent as the same becomes better understood by reference to the following detailed description.

In the present method of making titanium alloys, very fine titanium powder (one to three microns) is needed in order to make satisfactory dispersions. As ordinary comminution techniques cause oxygen embnittlement, a special technique using titanium hydride is employed. Titanium hydride is produced by reacting grade A-l titanium sponge with high purity hydro-gen at an elevated temperature. While hydrogen is known to embrittle titanium the hydrogen can be removed by vacuum treatment at elevated temperature. The hydride sponge is ball milled inside a helium atmosphere chamber having a dew point ranging between -20 and --50 degrees F. The average size of the milled particles is about 2.5 microns and this is used as the base material.

The intermeta'llic compounds 'Ili Si TiB TiC, and TiAl have been successfully alloyed with titanium to increase its mechanical properties. These intermetallic compounds have a particle size, in the as-received condi tion, which is too large for use in dispersion strengthening. Consequently, it is necessary to grind these powders to as fine a particle size as possible. One method of accomplishing this is by "long time ball milling in methanol in a porcelain mill using hardened steel balls as the grinding medium. As the milling time is usually about 300 Patented Sept. 4, 1962 hours, the wear on the balls is quite high and it may be necessary to remove the iron from the powder. This can be accomplished by leaching the ground powder in 1:1 HCl until the filtrate shows no color with potassium cyanide (KCN). The leaching operation normally takes about 24 hours. After the leaching operation, the powder is washed with methanol and air dried.

Blending of the titanium hydride and the intermet-allic compounds is also accomplished by a ball milling operation. The product of this operation is then put in a retort for vacuum outgassing treatment at 1100 degrees F. for approximately 16 hours. Consolidation can be accomplished by vacuum hot pressing, by cold compaction and extrusion, or by cold compaction, sintering and extrusion. All milling of the powder and loading of the dies is done in a chamber containing an inert atmosphere and the dies are transferred to the furnace in a protective bag.

EXAMPLE I Titanium hydride is ball milled for approximately 16 hours to reduce the average particle size to l-3 microns in size. Tapping the ball mill during rotation prevents the hydride powder from packing 7 percent by volume of the intermetallic compound TiAl is added to the titanium hydride and the mixture is ball milled for approximately 8 hours. The product is then consolidated by cold compaction. The formed billets are next extruded at 1800 degrees F. to the desired shape and annealed 2 hours at 1300 F. in a vacuum. The hardness of the alloy at various temperatures is shown in Table I. This table gives hardness values for the product as extruded, and also after annealing for 18 hours at 1300 degrees F.

EXAMPLE Il[ Same as Example I except that 6.3 percent by volume of the intermetallic compound Ti Si is alloyed with the titanium instead of the intermetallic compound TiAl. The particle size of the Ti Si is approximately 0.8 micron before mixing with the titanium. Table 11 lists the hardness of the alloy for three conditions, namely: as extruded and annealed 2 hours at 1300 F.; after annealing for 4 hours at a temperature of 1380 degrees F.; and after annealing for 4 hours at a temperature of 15 60 degrees F. Table III lists the tensile properties of the alloy at various temperatures.

EXAMPLE I-II Same as Example I except that 5.5 percent by volume of the intermetallic compound TiC is alloyed with the titanium instead of the intermetallic compound TiAl. Table IV lists the value for hot hardness of the alloy at various temperatures. This table gives the value for hot hardness in the as extruded and annealed condition and also for an alloy that has been compacted, sintered, and extruded. Table V lists the value for hot hardness of an alloy having 5.5 percent by volume of TiC of which the average particle SiZe is approximately 0.6 micron. Table VI lists the tensile properties of the alloy at various temperatures. Table VII shows the results of stressrupture tests at various temperatures.

EXAMPLE IV Same as Example I except that 6.2 percent by volume of the intermetallic compound TiB is alloyed with the titanium instead of the intermetallic compound TiAl. The particle size of the TiB is approximately 0.6 micron before mixing with the titanium. Table VIII shows the hot hardness of the alloy at various temperatures, and for two conditions, namely: in the as-extruded and annealed condition, and after annealing for 4 hours at a temperature of 1560 degrees F.

Table I HOT HARDNESS [7.0 percent by v. of TiAl] Cold compacted, ex- Cold compacted, ex-

truded and annealed truded and annealed 2 hours at 1,300 F. 18 hours at 1,300 F.

Temp. F. DPH Temp. F. DPH

RT 478 RT 356 Table 11 HOT HARDNESS [6.3 percent by v. of Ti si TENSILE PROPERTIES [6.3 percent by v. of Ti si Cold compacted, extruded and anneale 2 hours at 1,300 F.]

Tensile Elongation Reduction Temp. F. strength (percent) in area (p.s.1.) (percent) Table IV HOT HARDNESS [5.5 percent by v. of T10 microns)] Cold compacted, Cold compacted, Cold compacted, extruded and sintered, extruded extruded and annealed 2 hours and annealed 2 hours annealed 18 hours at 1,300 F. at 1,300 F. at 1,300 F.

Temp. F. DPH Temp. F. DPH Temp. F. DPH

RT 442 RT 435 RT 521 632 116 431 210 632 271 812 107 619 185 818 225 922 80 826 125 930 166 1, 002 62 998 84 1, 011 134 1, 201 29 1, 218 41 1, 207 46 1, 398 12 1, 411 21 4 Table V HOT HARDNESS [5.5 percent by v. of TiO (0.6 micron)] Cold compacted, slntered, extruded and annealed 2 hours at 1,300 F.

Temp. F. DPH

Table VI TENSILE PROPERTIES [5.5 percent by v. of TiO (5). Cold compacted, sintered, extruded and annealed 2 hours at 1300 F.]

Tensile strength (p.s.1.)

Elongation (percent) Temp.

Table VII STRESS-RUPTURE LIFE [5.5 percent by v. of TiC (51). Cold compacted, sintered, extruded and annealed 2 hours at 1300 F.]

Temp. F. Stress (p.s.i.) Life (hours) Table VIII HOT HARDNESS [6.2 percent by v. of Tim] Cold compacted, ex-

truded and annealed 2 hours at 1,300 F.

Cold compacted, extruded and annealed 4 hours at 1,560 F.

Temp. F. DPH Temp. F. DPH

DPH:

where:

DPH=diamond pyramid hardness L=load in kilograms d=length of diagonal in mm.

Tables III and VI show the results of tensile tests which were made using standard equipment. Elevated temperature tests were conducted by heating the specimen to the required temperature followed by a soaking period of 15 minutes. No protective atmosphere was used during the test.

Table VII shows the results of stress-rupture tests which were conducted using constant load machines. The specimens were heated to the testing temperature and allowed to soak a minimum of 15 minutes before the load was applied. No protective atmosphere was used during the test.

.The mechanical properties of unalloyed titanium are shown in Tables IX, X and XI.

Table IX HOT HARDNESS [Unalloyed Titanium (2.5M

Temp. F DPH 77 259 454 155 818 90 1017 60 1107 48 Table X TENSILE STRENGTH [Unalloyed Ti (2.5a TiH). Cold compacted, extruded and annealed 2 STRESS-RUPTURE LIFE [Unalloyed Ti (2.5;; TiH). Cold corrggaeted, extruded and annealed 2 hours at 130 F.]

Temp. F. Stress Life Elongation (hours) (percent) By comparing the data in Tables I to VIII with the data for unalloyed titanium (Tables IX to XI) it can be seen that the dispersion strengthening of titanium by the addition of intermetallic compounds is feasible. For example, at room temperature, the hot hardness of an alloy containing 7 percent of the intermetallic compound TiAl is shown to have a DPH value of 478, as compared to 259 for unalloyed titanium. By way of another example, at a temperature of 1200 degrees F., the tensile strength of an alloy containing 6.3 percent of the intermetallic compound Ti Si is 46,200 p.s.i., as

compared to a tensile strength of 15,950 psi. for unalloyed titanium.

It can thus be seen that the present invention discloses new and useful alloys and a method of preparing them. Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is, therefore, to be understood that the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. Sintered titanium base alloys comprised of from about 5 percent to about 7 percent, by volume, of an intermetallic compound having a grain size of from about 0.5 micron to about 5 microns, said intermetallic compound being selected from the group consisting of Ti Si TiB TiC, and TiAl, balance titanium having a grain size of from about 1 micron to about 3 microns, said intermetallic compound being dispersed in said titanium and said alloys being characterized by improved strength at high temperature and by increased hot hardness, as compared with unalloyed titanium.

2. A titanium base alloy comprised of about 6.3 percent, by volume, of the intermetallic compound Ti Si having a grain size of from about 0.5 micron to about 5 microns dispersed in about 93.7 percent, by volume, of titanium having a grain size of from about 1 micron to about 3 microns, said alloy being characterized by improved strength at high temperature and by increased hot hardness, as compared with unalloyed titanium.

3. A titanium base alloy comprised of about 6.2 percent, by volume, of the intermetallic compound TiB having a grain size of from about 0.5 micron to about 5 microns dispersed in about 93.8 percent, by volume, of titanium having a grain size of from about 1 micron to about 3 microns, said alloy being characterized by improved strength at high temperature and by increased hot hardness, as compared with unalloyed titanium.

4. A titanium base alloy comprised of about 5.5 percent, by volume, of the intermetallic compound TiC having a grain size of from about 0.5 micron to about 5 microns dispersed in about 94.5 percent, by volume, of titanium having a grain size of from about 1 micron to about 3 microns, said alloy being characterized by improved strength at high temperature and by increased hot hardness, as compared with unalloyed titanium.

5. A titanium base alloy comprised of about 7 percent, by volume, of the intermetallic compound TiAl having a grain size of from about 0.5 micron to about 5 microns dispersed in about 93 percent, by volume, of titanium having a grain size of from about 1 micron to about 3 microns, said alloy being characterized by improved strength at high temperature and by increased ho-t hardness, as compared with unalloyed titanium.

References Cited in the file of this patent UNITED STATES PATENTS 2,852,366 Jenkins Sept. 16, 1958 FOREIGN PATENTS 735,472 Great Britain Aug. 24, 1955 OTHER REFERENCES Metal Progress, v. 55, March 1949 (pp. 359-361 relied upon).

Treatise on Powder Metallurgy, vol. II, Goetzel Interscience Publishers, Inc., New York, 1950 (pp. 699 relied on).

Constitution of Binary Alloys, 2nd ed., Hansen, Mc- Graw-Hill Book Co., Inc., 1958 (pp. 140, 262, 384, 1198 relied on).

Light Metals, v01. 19, No. 215, February 1956, pp. 60-63. 

1. SINTERED TITANIUM BASE ALLOYS COMPRISED OF FROM ABOUT 5 PERCENT TO ABOUT 7 PERCENT, BY VOLUME, OF AN INTERMETALLIC COMPOUND HAVING A GRAIN SIZE OF FROM ABOUT 0.5 MICRON TO ABOUT 5 MICRONS, SAID INTERMETALLIC COMPOUND BEING SELECTED FROM THE GROUP CONSISTING OF TI5SI3, TIB2, TIC, AND TIAL, BALANCE TITIANIUM HAVING A GRAIN SIZE OF FROM ABOUT 1 MICRON TO ABOUT 3 MICRONS, SAID INTERMETALLIC COMPOUND BEING DISPERSED IN SAID TITANIUM AND SAID ALLOYS BEING CHARACTERIZED BY IMPROVING STRENGTH AT HIGH TEMPERATURE AND BY INCREASED HOT HARDNESS, AS COMPARED WITH UNALLOYED TITANIUM. 